• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.41-54
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• 2024

Regular monitoring plays a crucial role in ensuring the safety of geotechnical structures. Currently, nondestructive methods are employed to monitor such structures to minimize the impact, e.g., sensor-based accelerometers, displacement meters, image-based lasers, and drone imaging. These technologies can observe surface changes; however, they frequently suffer difficulties in terms of identifying changes in internal properties. To monitor changes in internal properties, in situ geotechnical investigations can be employed. A nondestructive test that can be used for this purpose is the spectral analysis of surface wave (SASW) test using geophones. The SASW test is a nondestructive method; however, due to the time required for data interpretation and the difficulty in analyzing the data, it is challenging to use the SASW test for monitoring applications that require frequent observations. However, it is possible to apply the first-step analysis, which yields the dispersion curve, for monitoring rather than the complete SASW analysis, which yields the shear wave velocity. Thus, this paper presents a fundamental study on the phase difference that derives the dispersion curve to utilize the SASW test for monitoring. The reliability of each phase difference interval is examined to determine the boundary to the subjected monitor. The study used phase difference data obtained using a geophone from a single-layered, homogeneous ground site to evaluate reliable boundaries. The findings of this study are expected to improve the utility of monitoring by identifying the ideal boundary for phase difference data.

• Korean Journal of Food Science and Technology
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• v.26 no.1
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• pp.88-92
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• 1994

The influence of the storage temperature between $0^{\circ}C$ and $30^{\circ}C$ on the biochemical, physical changes and meat qualities in the red muscle(M. sternomandibularis and M. mastoideus) of Korean native cattle postmortem were studied. The results obtained were summarized as follows; The pH-value during the first hours post mortem was dropped faster in storage temperature $0^{\circ}C$ than in $10^{\circ}C$, but the final pH-value reached after about 30 hrs. post mortem. The muscle which was stored in $30^{\circ}C$ reached the final pH within 10 hrs. The muscle which was stored in $0^{\circ}C$ showed the increased R-value at fast speed from the beginning. It reached maximum R-value after 20 hrs as it gradually increase showing low R-value by 10 hrs. in $10^{\circ}C$. The muscle which was stored in $0^{\circ}C$ shortened to about 46% after 10 hrs. It was contracted about 17% after 15 hrs in $10{\sim}20^{\circ}C$. The sarcomere length of Korean native cattle had the least contraction in $10^{\circ}C$ and it was contracted $18{\sim}20%\;(1.60{\sim}1.63\;{\mu}m)$ after 5 hrs., $45{\sim}46%$after 24 hrs in $0^{\circ}C$ and $30^{\circ}C$ which was generated cold shortening and rigor shortening. The meat that was stored in $0^{\circ}C$ and $30^{\circ}C$ showed about 2-fold higher shear force than it that was stored in $10^{\circ}C$ at postmortem 24 hrs. The meat that was stored in $10^{\circ}C$ at postmortem 24 hrs. showed drip loss less than 3% during the 9 days ripening period. The meat with cold shortening and rigor shortening showed the high drip loss.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.1
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• pp.115-123
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• 1990

The purpose of this study was to examine the uses of coal ash as a type of construction material. The methods of examination were chemical anlysis, soil laboratory test and the soil vibration test. Materials used were coal ash obtained as a by-product from 5 thermal power plants in Yongdong, Yongwol, Sochon(anthracite coal) and in Samchonpo and Honam (bituminous coal). Over 70% of the coal ash consisted of silica and alumina. The fly ash grain size showed a uniform distribution from fine-sand to silt, and that of the bottom ash showed from sand to gravel. The specific gravity and density of the coal ash were low. The long term strength increased gradually due to the self-setting property resulting from pozzolanic activity. The shear strength was higher than that of general soil. Cohesion and optimum moisture content of anthracite coal ash were higher than bituminous coal ash, whereas the maximum dry density was higher in bituminous coal ash. The coal ash dynamic Young's modulous curve range was similar to that of general soil. Of the results from the soil vibration test by car-running, the size relative acceleration level in the ash pond was higher than that of natural ground, but the damping ratio was lower than that of natural ground near the ash pond. The coal ash has more advantageous engineering properties than general soil with particles of the same size. For example, the California Bearing Ratio of the bottom ash at both Yongdong and Yongwol was 77~137%. Therefore we expect that if further study is done, coal ash can be used as a construction material when reclaiming seashore, construction embankments, road construction, making right-weight aggregate, or as a general construction material.

• Applied Chemistry for Engineering
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• v.5 no.4
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• pp.681-697
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• 1994

The enzymatic hydrolysate of gelatin extracted from fish skin was fractionated and recycled through the membrane reactor according to the molecular weight for the purpose of using as functional material. In addition, the enzymatic hydrolysis conditions of gelatin, enzyme stability by membrane and mechanical shear, and effect on the long-term operational stability of the recycle membrane reactor were investigated. Using the pH-drop technique, Alcalase, pronase E and collagenase were identified as the most suitable enzymes for the hydrolysis of fish skin gelatin. The optimum hydrolysis conditions in the 1st-step membrane reactor(1st-SMR) by Alcalase were enzyme concentration 0.2mg/ml, substrate-to-enzyme ratio(S/E) 50(w/w), $50^{\circ}C$, pH 8.0, reaction volume 600ml and flow rate 6.14ml/min. In the 2nd-SMR by pronase E were enzyme concentration 0.3mg/ml, S/E 33(w/w), $50^{\circ}C$, pH 8.0, reaction volume 600ml and flow rate 6.14ml/min. In the case of 3rd-SMR, enzyme concentration 0.1mg/ml, S/E 100(w/w), $37^{\circ}C$, pH 7.5, reaction volume 600ml and flow rate 10ml/min. Decreased enzyme activities by mechanical shear and membrane were 30% and 15% in the 1st-SMR, were 14% and 5% in the 2nd-SMR, and 18% and 8% in the 3rd-SMR, respectively. Under the optimum conditions, the degree of hydrolysis in the 1st, 2nd and 3rd-SMR were 3.5%(Kjeldahl method, 87%), 3.1%(77%) and 2.7%(70%), respectively. The productivity of hydrolysate in the continuous three-step membrane reactor was 430mg per enzyme(mg) for 10 times of volume replacements.

• The Journal of the Petrological Society of Korea
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• v.28 no.3
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• pp.157-169
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• 2019

Pseudotachylytes, produced by frictional heating during seismic slip, provide information that is critical to understanding the physics of earthquakes. We report the results of occurrence, structural characteristics, scanning electron microscopic observation and geochemical analysis of pseudotachylytes, which is presumed to have formed after the Late Cretaceous in outcrops of the Paleoproterozoic granitic gneiss on the Bulil waterfall of the Jirisan area, Yeongnam massif, Korea. Fault rocks, which are the products of brittle deformation under the same shear stress regime in the study area, are classified as pseudotachylyte and foliated cataclasite. The occurrences of pseudotachylyte identified on the basis of thickness and morphology are fault vein-type and injection vein-type pseudotachylyte. A number of fault vein-type pseudotachylytes occur as thin (as thick as 2 cm) layers generated on the fault plane, and are cutting general foliation and sheared foliation developed in granitic gneiss. Smaller injection vein-type pseudotachylytes are found along the fault vein-type pseudotachylytes, and appear in a variety of shapes based on field occurrence and vein geometry. At a first glance fault vein-type seudotachylyte looks like a mafic vein, but it has a chemical composition almost identical to the wall rock of granitic gneiss. Also, it has many subrounded clasts which consist predominantly of quartz, feldspar, biotite and secondary minerals including clay minerals, calcite and glassy materials. Embayed clasts, phenocryst with reaction rim, oxide droplets, amygdules, and flow structures are also observed. All of these evidences indicate the pseudotachylyte formed due to frictional melting of the wall rock minerals during fault slip related to strong seismic faulting events in the shallow depth of low temperature-low pressure. Further studies will be conducted to determine the age and mechanical aspect of the pseudotachylyte formation.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.21-30
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• 2011

As well known, dowel bars are used to transfer traffic load acting on one edge to another edge of concrete slab in concrete pavement system. The dowel bars widely used in South Korea are round shape steel bar and they shows satisfactory performance under bending stress which is developed by repetitive traffic loading and environment loading. However, they are not invulnerable to erosion that may be caused by moisture from masonry joint or bottom of the pavement system. Especially, the erosion could rapidly progress with saline to prevent frost of snow in winter time. The problem under this circumstance is that the erosion not only drops strength of the steel dower bar but also comes with volume expansion of the steel dowel bar which can reduce load transferring efficiency of the steel dowel bar. To avoid this erosion problem in reasonable expenses, dowers bars with various materials are being developed. Fiber reinforced plastic(FRP) dower that is presented in this paper is suggested as an alternative of the steel dowel bar and it shows competitive resistance against erosion and tensile stress. The FRP dowel bar is developed in tube shape and is filled with high strength no shrinkage. Several slab thickness designs with the FRP dowel bars are performed by evaluating bearing stress between the dowel bar and concrete slab. To calculated the bearing stresses, theoretical formulation and finite element method(FEM) are utilized with material properties measured from laboratory tests. The results show that both FRP tube dowel bars with diameters of 32mm and 40mm satisfy bearing stress requirement for dowel bars. Also, with consideration that lean concrete is typical material to support concrete slab in South Korea, which means low load transfer efficiency and, therefore, low bearing stress, the FRP tube dowel bar can be used as a replacement of round shape steel bar.

• Journal of the Korean earth science society
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• v.37 no.4
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• pp.218-229
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• 2016

The bedform stability diagram indicates the shape and size of bedforms that will occur to a given grain size and flow velocity. The diagram has been constructed from experimental data which have been mostly acquired by flume experiments. Generally, the flume experiments have been performed on well sorted sediments with unimodal grain size distribution, in order to understand relationship between grain size and flow velocity. According to the diagram, a ripple structure initiates to be formed from lower flow regime flat bed, as the flow velocity increases on the surface of fine-sand or medium-sand sediments. This study aims to verify that the experimental result of bedform stability diagram will be reproduced in our flume experimental systems, and also to confirm that the result is consistent not only on well-sorted sand sediments but also on poorly-sorted sand sediments with bimodal grain size distribution. The experimental results in this study show that initiation of 2D or 3D ripple structure on poorly-sorted sand sediments requires higher flow velocity and shear stress than those for initiation of the structure on well-sorted sand sediments. In general, carbonate sediments are characterized by poor sorting due to inactive hydraulic sorting and bimodal grain size distribution with allochems and matrices. The results suggest that the carbonate depositional system possibly need a higher flow velocity for initial formation of 2D or 3D bedform structures. The reason might be the fact that pulling off and lifting of a grain in poorly sorted sediments require more energy due to sorting, friction, stabilization, armour effects, and their complex interaction. This preliminary study warrants additional experiments under various conditions and more accurate analysis on the relationship between formation of bedforms and grain size distribution.

• The Journal of Engineering Geology
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• v.7 no.3
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• pp.191-205
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• 1997

Measurements on subsurface movement of the Songsanri tomb site including the Muryong royal tomb was conducted using a tiltmeter system for the period of 15 months form July 7, 1996 to September 30, 1997. Two coordinate tilt monitoring data shows the biggest movement rate of 2.3mm/m/yr toward south in the frontal wall(N-S tilt) of the Muryong royal tomb. Southward tilting of bricks above the southern fire place in the western wall of the Muryong royal tomb is a proof of southward tilting of the royal tomb since its excavation in 1971. The eastern wall of the Muryong royal tomb is also tilting toward inside the tomb with the rate of 1.523mm/m/yr. Furthermore, tilting rate of wall increases twice in rainy season. It is interpreted tbat infiltration of water into the tomb and nearby ground in rainy season results in dangerous status for the safety of tomb structure. On the whole, normal component tilting of the walls of the 5th tomb is large than its shear component. It shows a small displacement toward one direction without no abrupt change in its direction and amount of tilting. The tilting rate of walls of the 6th tomb is about 8.8mm/m/yr in the dry season which is much bigger than those of other tombs in rainy season. Deformation events of walls of the tombs are closely related to amount of precipitation and variation of temperature. In comparison with different weather conditions, tilting is much bigger during the period of rainy weather than sunny weather. It is interpreted that rainwater flew into the turm through faults and nearby ground. High water content in nearby ground resulted strength of ground. The tilting event of walls shows a hysterisis phenomenon in analysis of temperature effect on tilting event. The walls tilt rapidly with steep rising of temperature, but the tilted walls do not come back to original position with temperature falling. Therefore, a factor of steep increase of the temperature must be removed. It means the tomb have to be kept with constant temperature. The observation of groundwater level using three boreholes located in construction site and original ground represented that groundwater level in construction site is higher than that of original ground during the rainy season from the end of June to August. It means that the drainage system of the Muryong royal tomb is worse than original ground, and it is interpreted that the poor drainage system is related to safety of tomb structure. As above mentioned, it is interpreted that artificial changes of the tomb environment since the excavation, infiltration of rainwater and groundwater into the tomb site and poor drainage system had resulted in dangerous situation for the tomb structure. According to the result of the long period observation for the tomb site, it is interpreted that protection of the tomb site from high water content should be carried out at first, and the rise of temperature by means of the dehumidifier inside the tomb must be removed.

• Geophysics and Geophysical Exploration
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• v.14 no.1
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• pp.98-104
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• 2011

Numerical simulation in exploration geophysics provides important insights into subsurface wave propagation phenomena. Although elastic wave simulations take longer to compute than acoustic simulations, an elastic simulator can construct more realistic wavefields including shear components. Therefore, it is suitable for exploration of the responses of elastic bodies. To overcome the long duration of the calculations, we use a Graphic Processing Unit (GPU) to accelerate the elastic wave simulation. Because a GPU has many processors and a wide memory bandwidth, we can use it in a parallelised computing architecture. The GPU board used in this study is an NVIDIA Tesla C1060, which has 240 processors and a 102 GB/s memory bandwidth. Despite the availability of a parallel computing architecture (CUDA), developed by NVIDIA, we must optimise the usage of the different types of memory on the GPU device, and the sequence of calculations, to obtain a significant speedup of the computation. In this study, we simulate two- (2D) and threedimensional (3D) elastic wave propagation using the Finite-Difference Time-Domain (FDTD) method on GPUs. In the wave propagation simulation, we adopt the staggered-grid method, which is one of the conventional FD schemes, since this method can achieve sufficient accuracy for use in numerical modelling in geophysics. Our simulator optimises the usage of memory on the GPU device to reduce data access times, and uses faster memory as much as possible. This is a key factor in GPU computing. By using one GPU device and optimising its memory usage, we improved the computation time by more than 14 times in the 2D simulation, and over six times in the 3D simulation, compared with one CPU. Furthermore, by using three GPUs, we succeeded in accelerating the 3D simulation 10 times.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.3
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• pp.43-52
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• 1984

This paper is concerned with the strain characteristics of the time effect on the remoulded saturated day sampled from the downstream of the Yeongsan river, and the constitutive equation that can generally explain time-dependent behaviors of norma1ly consolidated clay. This paper examines whether or not the afore-said constitutive equation can be applied to the remoulded Mooan-clay. Throughout this study, the conclusions obtained are as follows. 1. Throughout the isotropic consolidation test for 7 days and the isotropic relaxation test, the existence of the static and dynamic yielding surfaces is confirmed respectively. 2. The characteristics of time effect of the deformation, namely, the existence of a unique stress-strain-time relation, is conformed from the experimental result on the Mooan-clay. 3. The prodictions of the stress path and the strain on the Cam-clay theory is not consistent with those observed during the experiments. 4. Constitutive equation(2-3-12) obtained by applying Cam-clay theory to Perzyna's elastic-viscoplasticity theory can explain the behavior of pore water pressure during isotropic stress relaxation, concerned with time dependency under undrained condition. The equation can also explain the results of the undrained triaxial compression test for the clay with different strain rate under the same or different consolidation history. 5. This constitutive equation has eight material parameters which can be determined from triaxial compression tests.